DE3440390A1 - OPTICAL FUNCTIONAL ELEMENT AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

The invention relates to an optical functional element that utilizes a thin-film optical waveguide and also a method for manufacturing the optical functional element.

So far, research activities have been carried out to find a thin film optical element using an optical fiber for various devices, e.g. as a light deflection device, light modulator, spectrum analyzer, Use correlator, optical circuit, etc. Such a thin film optical element has a function of refractive index of the fiber optic cable due to external influences, for example through the acoustic-optical effect, electro-optical Effect, etc. to change, thereby modulating or modulating the light propagating in and through the optical waveguide is distracted. Suitable substrates for the formation of the above optical element are lithium niobate crystals

/ 25

Dresdner Biink (Munich} account u939 844

Bayer VereiiisOank (Munich) loo. 508 941

Postal check (Munich) account 670-43-804

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(LiNbO.,) And lithium tantalate crystal (LiTaO ₃ ), which are excellent in piezoelectric properties, acousto-optic effect and electro-optic effect and have a low light propagation loss, have been widely used.

As a representative method for manufacturing the thin film optical waveguide using the aforementioned

-J ₁ Q th crystal substrate, a method has been known in which titanium (Ti) is thermally diffused at a high temperature on the surface of the above-mentioned crystalline substrate, whereby on the surface of this crystalline substrate, an optical waveguide layer with a

₁ c refractive index is formed, which is slightly larger than that of the substrate. However, the thin film optical waveguide manufactured by this method has various disadvantages. So it is easily subject to optical damage and you can only enter the waveguide path

_ ■ introduce a very small light output. Under the expression "Optical damage or error", as used in the description, is to be understood as a phenomenon in which the light intensity that propagates in and through the optical waveguide and then emitted to the outside is, because of its scattering proportional to the input light intensity, is not increased further when the in the optical fiber to be introduced is gradually increased.

A method for making an improved waveguide

ters, which is less likely to oU to optical damage

has become known in which the crystal substrate made of LiNbO, or LiTaO, is heat-treated at a high temperature is to diffuse lithium oxide (Li ^ O) outside the crystalline substrate, creating in the neighborhood A lithium (Li) -free intermediate layer with a refractive index is formed on the surface of the substrate

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which is slightly larger than that of the substrate.

R.L. Holman and P.J. Cressman in "IOC, 90, April 28 1981 "described that by the above-described external diffusion treatment of Li-O, the threshold value of the optical damage becomes higher than that achieved by internal diffusion treatment with Ti. If by chance the light deflector and the light modulator

■ LP using the acoustic-optical effect or the Electro-optical effect to be realized, increases the efficiency of each of the above mentioned effects represent an important factor in the formation of the element. As a representative example for the

jg use of the acoustic-optical effect there is a procedure, in which a high-frequency electric field to comb-shaped Electrodes is applied, which are formed by photolithography technology on the optical waveguide, so that elastic surface waves on the optical waveguide

_ _{n be} excited. It is known in this case that the interaction between the surface waves excited on the optical waveguide and the guided light which propagates in and through the optical waveguide is increased as soon as the energy distribution of the guided light is achieved

_{oc is} concentrated near the substrate surface. 2 B

(See CS. Tsai, "IEEE Transaction on Circuits, and Systems", Vol. CAS-26, 12, 1979.)

From the point of view of maximum utilization of the

The interaction mentioned above causes the thickness of the ο υ

Optical waveguide layer (a lithium-free gap _{layer) / to be} formed by the above-mentioned LI2O external diffusion method, small changes in the refractive index, so that the layer with a thickness of

10 to 100 / am must be produced. This is \ unfavorable, 35

because the energy distribution of the guided light is m

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Direction of the thickness of the layer spreads. Therefore, it was difficult to realize a high efficiency in the resulting device in which a Dünnf ilin-Wel lenleiter is utilized, as utilized by the above-described outer diffusion method using ^L i ₂ ° ^ ^ÜR ^ ^e Preparation of Lichtablenkgeräts etc. will.

On the other hand, another method is for preparing egg _{1 (~,} known nes improved thin-film waveguide having low optical damage by an ion exchange method. In this method, the crystal substrate is made of LiNbO, or LiTaO, at a low temperature to a heat treatment in a dissolved salt of tallium _{nitrate (CTlNO 3} ), silver nitrate (AgNO ₃ ), potassium nitrate (KNO ₃ ) and the like or in a weak acid such as benzoic acid (C _fi H, -COOH) is heat treated to release lithium ions (Li) in the crystalline substrate by an ion species in the weak acid, about to exchange protons (H). In this way, an optical waveguide layer having a large difference in refractive index (4h ^ 0.12) is formed.

While the thin film waveguide passing through the above described ion exchange process has been produced, has an improved property with respect to the threshold visual damage, which is some is ten times higher than the thin film optical waveguide obtained by titanium diffusion, but there is a problem that that the piezoelectricity and the electro-optical properties that the crystals of LiNbO, and LiTaO, are inherent, get worse by the ion exchange process ^ with the result that, for example, when using as a light deflection device, the refractive efficiency of the guided light is inevitably reduced.

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In view of the disadvantages described above, the object of the invention is to provide an optical functional element with a sufficiently high threshold value for its optisehe damage and with a sufficient one Light modulation or deflection can be carried out.

Furthermore, an improved method for producing such an optical functional element is to be provided.

The invention relates to an optical functional element with a substrate, an optical waveguide, which is connected to the surface of the substrate, except in an area of the same ^ is formed by an ion exchange process,

, p. andmeans attached to the portion of the substrate surface is provided with which no ion exchange process has been performed, and which modulates the light propagating in and through the optical waveguide or deflects by the refractive index of the optical fiber is changed by an external influence.

The invention is explained in more detail with reference to the drawing explained.

FIGS. 1 to 4 show perspective views of preferred FIGS

th embodiments of the optical according to the invention Functional element,

5A and 5B are schematic sectional views explaining an example of manufacturing the optical functional element according to the embodiment shown in FIG. 4.

Figures 6 through 9 illustrate perspective views of other embodiments of the optical functional element according to the invention.

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Figs. 10A to 10D are schematic sectional views of Figs Explain the production example of the optical functional element according to the embodiment shown in FIG. 9.

11 is a perspective view of another example of the optical functional element according to the invention.

Figs. 12A to 12C are schematic sectional views of Figs illustrate a production example of the optical functional element according to the embodiment shown in FIG. 11.

Fig. 1 illustrates a light deflection device according to a first embodiment of the optical according to the invention Functional element. In the drawing, the reference numerals mean the following: 1 a crystal substrate, 2 a through

“ _N ion exchange treated area for the formation of the optical waveguide, 3 a section that has not been treated by ion exchange, 4 a comb-shaped electrode on the output side, 5 a comb-shaped electrode on the receiving side, 6 an optical coupling input prism and

"P- 7 an optical coupling output prism. As shown in FIG is, the thin film optical waveguide is in the form of the Deflection device according to this embodiment distinguished by that it has comb-shaped electrodes on the portion not treated by ion exchange, the have the function of generating elastic surface waves or to receive.

The following is the method of manufacturing the light deflector explain this particular embodiment in more detail

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A surface (e.g. χ -.surface) of a LiNbO, crystal an X-plate (with a thickness of 1 mm in the direction of the x-axis and a length of 2.54 cm in the directions Q of the _z- and χ-axes) was reduced to a degree of flatness of a few Newton rings or less polished after ordinary ultrasonic cleaning with methanol, acetone and pure water, and then the surface was dried by a blower with nitrogen gas.

Subsequently, a 1 mm thick aluminum plate in the shape of area 2 of the substrate treated by an ion exchange method was placed on the LiNbO, substrate, whereupon chromium (Cr) and aluminum (Al) by vapor deposition to a thickness of 5.0 nm and 145 nm, respectively was deposited on it. As the substrate also LiTaO- can be used, thereby forming thin films of chromium and aluminum as a mask for the ion exchange method on the portion where the comb-shaped electrodes formed advertising _ ₀ to the.

In the next stage, the crystal substrate would be ion-exchanged with the aforementioned mask formed thereon. The ion exchange process was carried out by placing 80 g of benzoic acid (C ₆ H ₁ -COOH) in a 100 ml quartz beaker, then placing the crystalline substrate with the mask in the beaker with the surface with the mask facing up completely cover the beaker with an aluminum foil and then the beaker with its contents 30

is introduced into a heating furnace for 15 minutes at a temperature of 25O ⁰ C. Instead of benzoic acid, weak acids like palmitic acid (CH ₃ (CH ₇ ) ^ COOH), stearic acid (CH ₃ (CH ₂ I ₁₆ COOH), etc. and dissolved salts like AgNO ₃ , TlNO ₃ , TlSO., KNO ₇ and others can be used can be used. 4 '3

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After the above-mentioned heat treatment, the substrate is held using a quartz tool taken out of the substrate and washed with ethanol and then with acetone. With these solvents the on Benzoic acid crystals adhering to the surface of the substrate are easily dissolved. After the washing process, the for The protective mask made of chrome and aluminum provided for the ion exchange process is removed using an etching solution.

In order to examine the property of the optical waveguide manufactured in this way, a He-Ne laser beam having a wavelength of 632.8 nm was passed through a rutile prism _1F . introduced into the waveguide surface in the direction of the y-axis to determine the light propagation loss. As a result, a value of 1.5 dB / icm was obtained. The threshold value obtained for the optical damage was also very high and was 10 mW / mm when the He-Ne light was used.

After the measurement, the optical waveguide was washed and dried again, whereupon a positive photoresist was replaced by a Spin coating with a thickness of 1 to 1.5 / in on top was applied. After that, a contact exposure was made under “,. Use of the negative mask for the comb-shaped electrodes carried out and then the photoresist was developed in such a way that not only the area for the comb-shaped electrode was left. After washing, the optical waveguide was dried and placed in introduced a vacuum deposition device, which on

-fi

a vacuum pressure of 1.33 10 mbar was evacuated. After that, aluminum was using electron beam deposition deposited to a thickness of 1500 Λ. After vapor deposition the waveguide was immersed in acetone for a few minutes, causing the aluminum film on the photoresist to pass through

Lift off and the area for the comb-shaped elec-

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trode was formed on the optical waveguide. In this case, the comb-shaped electrode is designed so that the main wavelength of the elastic surface waves is 600 Hz. For this reason, the width of the comb-shaped electrodes and the space between the electrodes are each set at 1.45 µm. In this manner, comb-shaped electrodes were provided at the not treated by ion exchange region and thus jQ, a thin-film optical waveguide in the form of a light deflecting device ¹ manufactured.

On the other hand, the same comb-shaped electrodes, as mentioned above, formed on the optical fiber,

-e obtained by covering the entire surface of the substrate subjected to the above-mentioned ion exchange process without, however, the protective mask for the ion exchange process was envisaged. Using this optical waveguide and the inventive Optical waveguide, the refraction efficiency of the guided light was determined for comparison purposes. As in; Fig. 1 is shown, both optical waveguides were treated with the incident light 9, a He-Ne laser with a Wavelength of 632.8 nm was used and a high frequency power of 0.6 W was applied to the comb-shaped electrode 4 on the discharge side. The incident light 9 was passed through the light coupling input prism 6 in Light converted and diffracted by the elastic surface waves 8 generated by the comb-shaped electrode 4

were suggested on the delivery side. The diffracted light turns 30

output from the light coupling output prism 7. On the other hand, the surface elastic waves became in the comb-shaped Electrode 5 added on the receiving side, opposite to the comb-shaped electrode on the delivery side

is arranged, reducing the insertion loss of the elasti-35

see surface waves can be measured. The refractive

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The efficiency is 601 when the comb-shaped electrodes are provided on the non-ion-exchange treated area of the substrate according to the invention, while the refraction efficiency is 0.5 % when the comb-shaped electrodes are provided on the ion-exchange treated area. If the comb-shaped electrodes are provided on the area of the substrate not treated by ion exchange within the scope of the invention, the value is

^ q of the insertion loss of the elastic surface waves 17 dB, while the value is 40 dB when the electrodes are formed on the ion-exchange treated area are. From the above result it follows that when the comb-shaped electrodes are arranged on the ionic

^ c exchange treated area, the implementation ratio too the elastic surface waves due to decreased piezoelectricity of the crystal is decreased due to the ion exchange process, thereby reducing the diffraction efficiency of the guided light decreases.

As explained above, the light deflection device in this particular embodiment has a high threshold value the optical damage and a high refractive efficiency of the guided light.

In the manufacture of the light deflecting device in the above-described embodiment of the invention becomes the protective mask for the ion exchange process according to the ion exchange process is peeled off once and then the comb-shaped electrodes are put through them again

Ion exchange treated area formed. However, in order to reduce the number of process steps, such comb-shaped electrodes are manufactured by using the protective mask material for the above-mentioned ion exchange process,
d

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The following is the second embodiment of the invention optical functional element explained with reference to FIG. In this figure, those parts are g, which are identical to those in FIG. 1, are denoted by the same reference number. In Fig. 2, the reference numbers mean: 1 a crystal substrate, 2 an ion exchange treated area, 4 a comb-shaped electrode on the output side, 5 a comb-shaped electrode on the • j ^ Q receiving side, 10 a light coupling input refraction grid " ter, 11 a light coupling output diffraction grating, and an outer diffusion layer made of Li-O (lithium oxide).

A difference between the second and the first Aus-.g Guide form is that an outer diffusion layer 12 of Li-O between the treated by ion exchange Layer 2 and the substrate 1 is inserted and the comb-shaped electrodes are formed on this outer diffusion layer made of Li-O.

As mentioned above, the method of forming the optical waveguide with the aid of the external diffusion of Li-O and by ion exchange described in detail in Japanese Patent Application No. 202470/1982. This second inventive Embodiment is more advantageous compared to the first embodiment, as an optical waveguide can be obtained with a low propagation loss. During the manufacture of the light deflection device according to the second embodiment, the following Process steps carried out after cleaning the substrate:

The above-mentioned cleaned and dried substrate is set up on a holder made of fused quartz

and placed in a thermal diffusion furnace at 1000 C

brings. Dried oxygen (O ₂ ) was used as a gas atmosphere

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introduced into the diffusion furnace at a flow rate of 2 l / min. The furnace temperature was raised from room temperature to 1000 ⁰ C at a rate of 16 ° C / min. When the temperature in the furnace became constant one hour after the temperature rise, the furnace was kept at a temperature of 1000 ^° C. for 8 hours and thereafter the substrate was gradually transferred ^{to the second diffusion furnace kept at 600 ° C.} Thereafter, the power to the second diffusion furnace was stopped and the furnace was allowed to cool from 600 ° C. to room temperature. After an external diffusion treatment with Li — O, the process steps according to the first embodiment were repeated in the same sequence, ie the production of the protective mask for the ion exchange process, ion exchange process, cleaning, etching away of the mask and formation of the comb-shaped electrodes.

The optical waveguide thus produced was investigated its properties with respect to _on by a He-Ne laser beam having a wavelength of 632.8 nm in the waveguide surface with respect introduced a Rutilprismas its \ y_ direction with the aid and its light propagation loss was measured. A value of 1.0 dB / cm was obtained. The measured value of the refraction efficiency was 601, which was the same as that of the first embodiment.

In the following, the third embodiment is the _ori he inventive optical functional element by reference in

would take on Fig. 3 explained.

In Fig. 3, reference numeral 13 denotes a diffusion layer made of titanium (Ti). The other parts are just that

same as the second embodiment and they will ο ο

therefore with the same reference numerals as in the previous one Designated embodiment.

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The method of manufacturing the optical waveguide by titanium diffusion and ion exchange methods is described in "Optical Communication 42 (1982) 101 "by M. DeMicheli, J. Botineau P. Sibillot, D.B. Ostrowsky and M. Papuchon.

This third embodiment according to the invention has the advantage that an optical waveguide can be obtained whose propagation loss is lower than that in the -, Q first and second embodiments. In the preparation of the light deflecting device according to the third embodiment of the present invention was the following process steps carried out after cleaning the substrate:

, g A thin film made of titanium with a film thickness of 20 nm was made on the dried surface of the substrate by electron beam deposition educated. The substrate was then set up on a fused quartz holder and then in a thermal diffusion furnace

_nn 965 ⁰ C introduced. Dried oxygen gas (O ₀ ) was introduced into the diffusion furnace as a gas atmosphere at a rate of 1 liter / min. The temperature in the furnace was increased from room temperature to 965 ⁰ C at a rate of 16 ° C / min. When the oven temperature is an hour after

f. the temperature increase became constant, the holder became

held at 965 C for 2.5 hours. After that, the holder became a second heat diffusion furnace, operating at 600 ° C was held, transferred. Then the power to the second diffusion furnace was cut off and the furnace was turned off at 600C

allowed to cool to room temperature. After the thermal 30

Diffusion treatment of titanium became the procedures according to the first embodiment repeated in the same order, i.e. the manufacture of the protective mask for the ion exchange process, ion exchange process, cleaning, etching away the mask material and formation of the camshaped Electrodes. To examine the properties of the so

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A He-Ne laser beam was used to produce the optical waveguide with a wavelength of 632.8 nm introduced through a rutile prism into the waveguide surface in its y-direction, to determine the loss of light propagation. A value of 0.2 dB / cm was obtained. The threshold the optical damage was as high as 15 mW / mm, although the optical waveguide had a titanium diffusion layer. On the other hand, the refraction efficiency was 701 be, Q which is higher than that in the first and second embodiments.

4 illustrates a light deflection device according to the fourth embodiment of the op-.p according to the invention. table functional element in which the parts identical to FIG. 1 are denoted by the same reference numerals are. Reference is made to the detailed explanations. In Fig. 4 shows that which was not ion-exchanged Area 3, for the sake of simplicity, a predetermined area, the neighboring areas of the comb-shaped electrodes 4 and 5 includes. In reality, however, such non-ion-exchanged areas are only in near these electrodes. This fourth embodiment provides comb-shaped electrodes to an area with _ which no ion exchange process has been carried out. The difference from the first embodiment is that the area not treated by ion exchange is only the area covered by the electrodes.

Referring now to FIGS. 5A and 5B, 30th

the method y.xxr production of the light deflection device according to this fourth embodiment is explained in more detail.

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₊

A surface (for example the χ surface) of a LiNbO ₃ crystal of an X plate (with a thickness of 1 mm in the x direction and a length of 2.54 cm in the corresponding z and y directions) was on a Flatness - -

polished to a few Newton rings or less, followed by ordinary ultrasonic cleaning using Methanol, acetone and pure water has been carried out. Subsequently, the surface was using a blower Nitrogen gas dried.

Then a positive photoresist was applied by a spinner applied to a thickness of 1 to 1.5 µm and then contact exposure was carried out thereon performed using a negative mask for the comb-shaped electrodes and then the exposed Photoresist developed in such a way that not only the area intended for the comb-shaped electrode remained. After the washing process, the crystal treated in this way was dried and placed in a vacuum deposition device. _6

brings that to a vacuum pressure of 1.3 3 χ 10 mbar

was evacuated, and then aluminum was electron beam deposited deposited with a film thickness of 1,500 Λ. After the vapor deposition, the aluminum film became on the photoresist by turning it on for several minutes

dipping in acetone was removed by lifting off, and comb-shaped electrodes 4 and 5 were formed on the crystal substrate 1 as shown in Figure 5A. As the electrode material, Au, Ti, Cr, etc. can be used in place of Al. In this case, the comb-shaped electrode is designed so that the main wavelength of the elastic surface waves can become 600 Hz. For this reason, the width of the comb-shaped electrode and the space between the electrodes are each set at 1.45 μm .

Thereafter, the ion exchange process is carried out on the crystal

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Substrate carried out using the mask mentioned above.

The ion exchange process was carried out by placing 80 g of benzoic acid (CgH ₁ -COOH) in a 100 ml quartz beaker, arranging the crystal substrate with the mask in the beaker so that its surface with the mask faces up, then the beaker with a Seal the aluminum foil tightly and then place the beaker with its contents in a heating furnace, in which the beaker is kept at a temperature of 250 ° C. for 15 minutes. In this case, weak acids and dissolved salts as mentioned in the above first embodiment can be used instead of benzoic acid.

Following the above heat treatment, the 15th

Substrate taken out using a quartz tool to hold the substrate and with ethanol and then with Acetone purified. With these solvents the benzoic acid crystals, adhering to the substrate easily

to be resolved. In this way, the ion-20

Exchange formed area 2 for generating the optical waveguide formed on the crystal substrate 1 while the area not treated by ion exchange is located only in the vicinity of the comb-shaped electrodes 4 and 5.

The optical waveguide thus produced was developed with a view to

its properties examined by using a He-Ne laser beam with a wavelength of 632.8 nm onto the waveguide surface introduced in y-direction with the help of a rutile prism and its light propagation loss be -30

was true. A value of 1.5 dB / cm was obtained.

“The threshold value for optical damage was as high as 10 mW / mm with the He-Ne laser beam. Further, under the same conditions as in the first embodiment, FIG

Refraction efficiency determined. It got a value of around 35

high as 60% received. The insertion loss of the elastic

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see surface waves showed a value of 17 dB / cm.

Figure 6 illustrates the fifth embodiment according to the invention

rungsform, which is a further improvement of the above 5

represents fourth embodiment described. It is It is to be noted that in this figure the parts which are identical to those in FIG. 4 are denoted by the same reference numerals.

In the drawing: 1 means a crystal substrate made of /

LiNbO ₃ , 2 em area treated by ion exchange,

4 a comb-shaped electrode on the delivery side, 5 a comb-shaped electrode on the receiving side, 10 a light coupling input diffraction grating, 11 a light coupling output diffraction grating and 12 an outer diffusion 15

layer made of lithium oxide (Li ₂ O).

The difference between this fifth embodiment and the embodiment shown in Figure 4 is that the outer diffusion layer of Li ₉ O between the ion

Exchange treatment formed layer and the substrate is inserted, and that the comb-shaped electrodes are formed on the outer diffusion layer of Li ₉ O. Because of this structure, the optical functional element according to this particular embodiment has an advantageous one

low loss of propagation.

In the manufacture of this light deflection device, the following process steps are carried out after cleaning the substrate. After the substrate was cleaned and dried, it was set up on a holder made of molten glass and then placed in a heat diffusion furnace kept at 1,000 ° C. Dried oxygen (O ₉ ) was introduced as a gas atmosphere into the diffusion furnace at a flow rate of 2 l / min

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leads. The oven temperature rose from room temperature to

1000 ° C increased at a rate of 16 ° C / min. When the temperature in the oven became constant one hour after the temperature rise, the oven at the Tempe-5

temperature of 1,000 ° C for eight hours, and then the substrate was gradually transferred to a second heat diffusion furnace kept at 600 ° C. The power supply to the second diffusion furnace was then interrupted and the furnace was ^{allowed to cool from 600 °} C. to room temperature. After the external diffusion process of Li_0, the process steps were carried out in the same order as in the first embodiment, ie formation of the kaitim-shaped electrodes and proton exchange.

The optical waveguide thus prepared was tested under the same conditions as tested in the first embodiment and it was found that the light propagation loss is 1.0 dB / cm and the

Refraction efficiency was 6o%. 20th

FIG. 7 illustrates the sixth embodiment according to FIG Invention which is a further improvement on the fourth embodiment described above. In the

In the drawing, reference number 13 denotes one with titanium do-25

layer and reference numeral 2 "means one ion-exchange treated portion wherein protons have been injected into the titanium doped layer. The remaining parts are identical to the optical one

Functional element, as shown in Figure 6, so that 30th

they are denoted by the same reference numerals. That optical functional element of this sixth embodiment has the advantage that a lower loss of light propagation than achieved in the fifth embodiment

can be.
35

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During the production of the optical functional element according to this sixth embodiment according to the invention following process steps after cleaning the substrate

_ carried out. A thin film of titanium with a thickness of 5

20 manometers were formed on the dried surface of the substrate by electron beam deposition. Afterward the substrate was erected on a holder made of fused quartz and then placed in a heat diffusion furnace arranged, which was kept at 965 ° C. Dried oxygen gas (0 ") was added to the diffusion furnace as Gas atmosphere introduced at a rate of 1 l / min. The temperature in the oven was from room temperature increased to 965 ° C at a rate of 16 ° C / min.

When the oven temperature is one hour after the temperature ο

As the increase became constant, the holder was at 9 65 C 2.5 Held for hours. Thereafter, the holder was gradually moved to a second heat diffusion furnace, which at 600 ° C was held. After that, the power supply became the

Second diffusion furnace ended and the furnace was heated to 600 C 20th

Allowed to cool to room temperature. After the heat diffusion treatment of titanium, the procedures became as in the fourth embodiment in Fig. 4 with the following Sequence carried out: formation of the comb-shaped

Electrodes and proton exchange. With regard to the test 25

function of the properties of the optical waveguide produced in this way was a He-Ne laser beam with a wavelength of 632.8 nm through a rutile prism into the waveguide surface introduced with respect to its y-direction in order to determine the light propagation loss. It became a value

of 0.2 dB / cm. The threshold of optical damage was as high as 15mW / mm despite its presence the titanium diffusion layer. On the other hand, the refraction efficiency was determined to be 70%, which is higher than that in the fourth and fifth

Embodiments.

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FIG. 8 shows a schematic sectional view of an optical functional element according to the seventh according to the invention Embodiment in which the electro-optical effect

is used. In the drawing, the reference numbers mean: 5

1 a crystal substrate made of LiNbO, 2 ″ an area treated by ion exchange in which protons are converted into a layer doped with titanium have been injected, 13 the layer doped with titanium, in which titanium diffuses heat 10 and 11 a light coupling diffraction grating for

Input or output and 9 a laser beam. In this seventh embodiment, the laser beam 9 is in the optical waveguide introduced from the light coupling diffraction grating 10. The guided beam is through the phase grating, generated by the electro-optic effect, at

Application of a voltage to the comb-shaped electrode 24 is generated, and output from the light coupling output grating 11 to the outside. The element shown in Figure 8 is produced by the following process steps.

+

A surface part (for example, χ face) of a LiNbO crystal an X-plate (with a thickness of 1 mm in the x-direction and a length of 2.54 cm in the z and y directions) was reduced to a degree of flatness of a few Newton rings or polished underneath, after which the substrate by ordinary ultrasonic cleaning using methanol acetone and pure water has been purified; then the surface was dried by a blower with nitrogen gas.

Thereafter, a thin film of titanium with a thickness of

20 nm was formed on the washed and dried surface of the substrate by electron beam deposition. The substrate was then erected on a fused quartz fixture and then placed in a thermal diffusion furnace maintained at 965 ° C. Dried oxygen gas (0 _? ) Was added to the

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Diffusion furnace as a gas atmosphere at a flow velocity introduced at 1 l / min. The temperature in the oven was increased from room temperature to 965 ° C with a

Speed increased by 16 ° C / min- When the oven temperature -5

For one hour after the temperature increase became constant, the holding device was kept at 965 ° C. for 2.5 hours. Thereafter, the holding device has been moved to the second furnace in stages, which was maintained at 60O ⁰ C. then

the power supply to the second diffusion furnace was interrupted ο

chen and the furnace was allowed to cool from 600 C to room temperature, whereby the titanium diffusion layer 13 was formed on the crystal substrate 1. As heat-diffusible metals, V, Ni, Au, Ag, Co, Nb, Ge etc, be used.

After the titanium diffusion, the substrate was cleaned and dried. Thereafter, a positive photoresist was applied to the substrate using a spin coater applied with a thickness of 1 to 1.5 μm. Then '

then a contact exposure using a negative one Mask for the Kamnv-shaped electrode was carried out, after which the exposed photoresist was developed in such a way that that the area of the comb-shaped electrode was not left alone. After the washing process, the sub-

strat dried and introduced into a vacuum deposition device, which to a vacuum pressure of 1.33 χ 10 mbar had been evacuated and then aluminum was electron beam deposited to a film thickness of 1,500 ^ deposited. After the vapor deposition, the substrate became

immersed in acetone for a few minutes to lift off the aluminum film on the photoresist and around to form the area solely for the comb-shaped electrode on the substrate. In this case it is comb-shaped Electrode designed so that the electrode width and the gap between the electrodes with 2.2 .mu.m and the

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Transverse width is 3.8 ram and 3 50 electrode pairs are used will. The crystal substrate on which the comb-shaped electrode 24 had been formed was an ionic

g subject to exchange procedure. 9 8.85 g benzoic acid (C, H COOH) and 1.05 g of lithium benzoate (C, H COOLi) became uniform mixed and placed in an alumina crucible.

In this crucible, the above-mentioned crystal. Q substrate with electrodes placed and then the crucible and the substrate were placed in a hot oven at 250 C one Held for hour. By this method, protons were injected into the area of the crystal substrate 1, in where no comb-shaped electrode 24 had been formed, p. and the ion exchange region 2 "was formed.

When forming this ion exchange region 2 ″, it is desirable to use a mixture of carboxylic acid with a Degree of dissociation in the range of 10 to 10 and a substance to be used in which in the carboxylic acid group

the hydrogen atom has been replaced by lithium

(e.g. a lithium salt of a carboxylic acid) such as a mixture of benzoic acid and lithium benzoate. Suitable examples are mixtures of palmitic acid CH- (CH ₂ ) ,. _ .. COOH and lithium _{palmitate CH 0} (CH.) Ί .COOLi; and a

ZO ο 2. 14

Mixture of stearic acid CH ₃ (CH ₂ KgCOOH and lithium stear-

rat CH ₀ (CH ") ,, COOLi. In this case, the lithium i Z Lb

salt of the carboxylic acid in the desired manner in a JYbl component from 0.1% to 3%, based on the total mixture. After the ion exchange process, the Substrate removed using a quartz tool to hold the substrate, with ethanol and then cleaned with acetone. With these solvents, the crystals of benzoic acid and Lithium benzoate slightly dissolved.

-28- I) H 4 3 99

When an electrical potential of 6V to the comb-shaped Electrode 24 of the electro-optical element which was produced according to the above-mentioned process steps,

g was applied to diffract the guided light beam, a diffraction fraction of 90% could be obtained. Even if the electro-optical element is in the optical functional element (EO) effect is exploited, the formation of the electrodes would be in an area in which no ion exchange process

Q ren has been carried out, a lowering of the electro-optical Prevent the effect of the crystal and the element can therefore work with high efficiency. A such electro-optic element can be formed not only by the method described above, but

r- also step through the same process as those of the element shown in Figures 4 and 5. ·

In the seventh embodiment of the invention described above, an optical waveguide was made by ion emission

-. exchange procedure established. Furthermore, by heat diffusion of protons entering the substrate through the heat exchange process have been injected, an optical functional element can be obtained which has a higher threshold value for the optical damage. this will

- explained below.

Figure 9 illustrates the eighth embodiment of the invention optical functional element, in which the element is an acousto-optical (AO) thin film element. In In the drawing, the reference numbers mean: 1 a crystal substrate made of LiNbO ^, 22 a region doped with protons, formed by thermal diffusion of titanium and protons 23 a non-proton-doped region in which titanium has diffused in only through heat, 4 a comb-shaped electrode on the delivery side, 5 a comb-shaped

-29- DE 4399

mige electrode on the receiving side, 6 a light coupling input prism, 7 a light coupling output prism, 8 elastic surface waves, 9 a laser beam, 30 a

optical waveguide layer that dos 5

Crystal substrate 1 is formed. The laser light 9 is in the light guide layer 10 is introduced from the light coupling prism 6 and through the elastic surface waves 8 which are generated when a high frequency power (RF) is applied to the comb-shaped electrode. The bowed one Light is emitted to the outside through the light coupling prism 7. In this eighth embodiment of the invention the efficiency in generating the elastic surface waves 8 is high because the comb-shaped electrodes 4 and 5 are arranged on the region 23 in which no protons have diffused. As the fiber optic layer is formed by thermal diffusion of titanium and protons, the threshold value for optical damage is more characteristic Way high, so that the item is an excellent one

is an optical functional element.
20th

The following is an example for the production of the optical functional element according to the eighth of the invention Embodiment explained in more detail with reference to Figures 10A to IOD.

A surface part (e.g. X -surface) of a LiNbO-j crystal substrate 1 of an X plate (with a thickness of 1 mm in the x-direction and a length of 2.54 cm in

the z- and y-directions) was set to a degree of flatness of 30

polished a few Newton's ring numbers or below, after which the substrate was cleaned by conventional ultrasonic cleaning using methanol, acetone and pure water. After that, the surface was using a blower

Nitrogen gas dried.
35

-30- DE 4399

Thereafter, a titanium thin film having a thickness of 20 nm was formed on the thus cleaned and dried surface of the substrate by electron beam deposition. The substrate was then set up on a fused quartz holder and then placed in a heat diffusion furnace maintained at 965.degree. Dried oxygen gas (O) was introduced into the diffusion furnace as a gas atmosphere at a flow rate of 1 liter / min. Thereafter, the temperature in the oven was increased from room temperature to 965 C at a rate of 16 C / min. When the furnace temperature became constant one hour after the temperature rise, the holder was kept at 965 ° C for 2.5 hours. Thereafter, the holder to a second heat diffusion furnace was gradually transferred, which was maintained at 600 ⁰ C. Then the power supply to the second diffusion furnace was interrupted and the furnace was ^{allowed to cool from 600 °} C. to room temperature, whereby a titanium-doped layer 31 was formed on the crystal substrate 1, as shown in FIG. 10A. As the heat diffusible metal, V, Ni, Au, Ag, Co, Nb, Ge, etc. can be used.

Thereafter, a 1 mm thick aluminum plate in a shape corresponding to the area to be subjected to proton exchange treatment was placed on the above-mentioned crystal substrate, on which chromium and then aluminum were deposited by electron beam deposition to thicknesses of 5.0 nm and 145 nm, respectively became. With QQ these chrome-aluminum thin films, a mask 33 was formed on the crystal substrate 1 as shown in Fig. 10B. Then, the ion exchange process was performed on this crystal substrate on which the mask 33 was formed. For this purpose, 98.85 g of benzoic acid (C ₆ H ₅ COOH) and 1.05 g of lithium benzoate (CgH ₅ COOLi)

-31- DE 4399

mixed uniformly and placed in an alumina crucible. In this crucible, the above-mentioned crystal substrate with the mask was placed and then the crucible and substrate were kept in a hot oven at 250 ° C for one hour. Through this procedure protons were injected into the area of the crystal substrate where there was no masking 33 and on thus, the ion exchanged region 3 2 was formed. In the formation of this with ion exchange

th region 32, it is preferred to use a mixture of carboxylic acid with a degree of dissociation of 10 to 10 and a material in which the hydrogen atom in the carboxylic acid has been substituted by lithium (for example a lithium salt of the carboxylic acid) about a mi

quenching of benzoic acid and lithium benzoate. Examples of such a mixture are in that described above seventh embodiment listed. After the ion exchange process, the substrate was washed using a quartz tool to hold the substrate taken out and

cleaned with ethanol and then with acetone. With these solvents, the adhering to the substrate can Crystals of benzoic acid and lithium benzoate are easily dissolved. After the washing process, the masking was done 33, which were built up from the protective thin films of chromium and aluminum for the ion exchange process, with a Etching solution removed.

Subsequently, the above-mentioned substrate was put into a 30th

hot furnace and an annealing treatment at 35O ° C For 2 hours in a water vapor-containing, humid oxygen atmosphere generated by oxygen is supplied at a flow rate of 0.5 l / min through heated water that is in the hot Furnace was passed. As a result, by the ion exchange process, protons were introduced into the substrate by heat

-32- DE 4399

diffusion injected, creating a proton-doped area on the crystal substrate 1 in which titanium and protons have been diffused by heat and which are not

Clay-doped regions 23 were formed in which titanium 5

has been diffused in by heat alone.

After the annealing process, the infrared absorption spectrum of the substrate was measured. The result showed that the Light absorbance in the vicinity of 3,500 cm because of OH group was 0.4, which is not very different from was the value of 0.3 8 before the annealing treatment. On the other hand, the difference between the propagation constant was with the TE mode of vibration (in the case of the X-crystal plate was the direction of propagation in y-direction, while im - "■

Fall of the Y-crystal plate in the direction of propagation

x-direction) and the refractive index of the substrate 0.11 before the annealing treatment, which is 0.06 after the Annealing treatment has been reduced. The combination of the results of light absorption by the OH group and the 20th

Propagation constants as described above were confirmed by the fact that the total amount of protons in the crystal did not change much by the annealing process and protons were diffused into the interior of the crystal.
25th

After the annealing stage, the comb-shaped electrode 4 was with a main frequency of 400 MHz on the non-proton-doped area 23 of the substrate with the aid of a conventional Photolithography process formed as it is in figure

IOP is shown.

When a high frequency power of 400 MHz to the comb-shaped Electrode 4 of the optical thin film element thus produced according to the invention was applied and light with 35

-33- DE 4399

at a wavelength of 6 3 2.8 nm was introduced into the element in order to reduce the diffraction efficiency of this To test light, the diffraction efficiency was 80%,

when the high frequency power was 600 mW. 5

On the other hand, the insertion loss was elastic Surface waves generated by the comb-shaped electrode 5 measured at the receiving side, 15 dB in the case of the present eighth embodiment. This value is considerable lower than the value of 40 dB in the case of the comb-shaped electrode formed on the area have diffused into the protons.

A measurement of the threshold value of the optical

Damage to both optical functional elements according to this embodiment according to the invention and the known embodiment which had a titanium-doped LiNbO ₃ optical waveguide. The laser beam used for the measurement was a He-Ne laser with a wavelength of 632.8

nm. In the case of the conventional optical functional element, optical damage occurred when the performance of the entered light reached a value of 0.1 mW / mm and above. In contrast, showed the invention optical functional element no optical damage until the power of the emitted light has a value of 1.7 mW / mm reached.

FIG. 11 is a perspective view of an optical functional element according to the invention according to the ninth Embodiment, wherein the structure shown in Figure 9 for a light deflection device using the electro-optical effect is applied. In the drawing, the reference numbers mean: 1 a crystal substrate made of LiNbO- ,, 22 a with Proton diffused area in which titanium and protons are diffused in by heat, 23 an area in which

-34- DE 4399

no protons have diffused in, i.e. in which titanium is alloine diffused in by heat, 24 a comb-shaped Electrode for the electro-optical effect, 10 and 11 a j-light coupling diffraction grating for input and output, respectively, 9 a laser beam; and an optical waveguide layer formed on the crystal substrate 1. In this ninth Embodiment according to the invention, the section 23 in which no protons have diffused only becomes nearby the comb-shaped electrode is formed. The laser beam 9 is guided into the light guide layer 30 from the light coupling diffraction grating 10. This directed ray becomes by a phase grating, which is created by the electro-optical effect when a voltage is applied to the comb-shaped

, _t electrode 24 is generated, and then diffracted by the light-5

coupling diffraction grating 11 released to the outside.

The following is an exemplary manufacturing process of the optical functional element of this ninth embodiment with reference to FIGS. 12A to 12C described.

First, a titanium diffused layer 31 was formed on the crystal substrate 1 made of LiNbO., As shown in FIG

Figure 12A in the same manner as in the eighth embodiment

is shown.

After the titanium diffusion, the substrate was then cleaned and dried, and then a positive photoresist with a thickness of 1 to 1.5 µm was applied using a ^r

Centrifugal applicator applied to it. Then became carried out a contact exposure using a negative mask for the comb-shaped electrode and the i.o obtained photoresist developed in such a way that not

only the comb-shaped electrode remained in it. After age 35

-35- DE 4399

Washing, the substrate was dried and placed in a vacuum deposition apparatus introduced, which was evacuated to a vacuum pressure of 1.3 3 χ 10 "" mbar. Subsequently was Aluminum by electron beam deposition with a Deposited film thickness of 150 nm. After vacuum deposition, the substrate was immersed in acetone for a few minutes, to remove the aluminum film on the photoresist. lift to remove and around the area 24 for alone HQ to form the comb-shaped electrode on the substrate. In this case, the comb-shaped electrode is designed so that the electrode width and the space between The electrodes are 2.2 yam, they are spaced apart by 3.8 mm and comprising 350 pairs of electrodes.

The crystal substrate on which the comb-shaped electrode 24 was formed was a proton exchange process subjected. In this case, the substrate was in a mixture of benzoic acid and lithium benzoate by the same Process steps as in the eighth embodiment heat-treated, whereby protons are injected into the area on which no electrode was formed, as shown in Fig. 12B, and thus became Layer 3 2 formed by ion exchange is obtained. Even

"P. Various materials can be used in this embodiment can be selectively used for the ion exchange process as in the eighth embodiment.

Then, the above-mentioned substrate was placed in a hot furnace and subjected to annealing treatment for two hours subjected to at 350 C in a moist, water vapor-containing oxygen atmosphere, which was thereby generated, that oxygen is supplied at a flow rate of 0.5 l / min through heated water that is in the hot

Furnace has been initiated. As a result, protons were in ob

-36- DR 4399

an area of the substrate diffused through heat,

on which no comb-shaped electrode was formed, whereby on the crystal substrate 1 the proton-doped region 22, in which titanium and protons diffuse and the non-proton-doped region 2 3 was formed in which titanium diffused by heat alone had been. In the course of this annealing treatment, there was no oxidation problem because the comb-shaped ElekjQ trode 24 was made of gold. According to the present embodiment, the manufacturing process is simplified, because the electrode acts as a mask for proton injection.

After the annealing treatment, a voltage of 6V was applied to the , e comb-shaped electrode of the electro-optical thus produced Element created to bend the introduced wave. A refraction efficiency of 90% was obtained.

The present invention is not limited to those described above different embodiments limited, but it can be used in various ways. In the above embodiments For example, LiNbO_ crystal was used as a substrate, but it is also possible to use the erp. inventive optical functional element according to exactly that same manufacturing process as mentioned above when lithium tantalate (LiTaO) is used as the crystal substrate. It is also possible that a light modulation device in the same way as in the preceding

Embodiments can be constructed. Furthermore, the 30th

Light modulation and the deflection of light also not only through the acousto-optical effect mentioned above or electro-optical effect but also by diffraction of magnetostatic surface waves, which

through the magneto-optical effect or through the thermo-35

-37- DE 4399

optical effect can be generated. Furthermore, the manufacturing method according to the invention has various variations possible. For example, if the material is one,

that during the heating process in manufacturing 5

stages of the aforementioned eighth embodiment not changed by itself, the comb-shaped electrode can be formed before the heating process. The inventive optical functional element can expediently for various devices and applications, for example as a photo scanner, can be used as a spectrum analyzer, correlator, etc.

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Claims (1)

Claims 1. Optical functional element with b) an optical waveguide, which is other than by ion exchange on the surface of the substrate thereof a range _/ formed and c) a device for bringing about a modulation or deflection of the propagating in the optical waveguide Light, the device being provided at an area on the surface of the substrate in which no Ion exchange has been carried out and which has the function of increasing the refractive index of the optical waveguide by external Change impact. 2. Functional element according to claim 1, characterized in that the substrate made of Lithiumnioba tkristall or lithium tantalate crystal is made. 3. Functional element according to claim 2, characterized in that the entire surface of the substrate is a Has been subjected to diffusion treatment with titanium. 4. Functional element according to claim 2, characterized in that that the entire surface of the substrate is external / 2 5 r Il.ml <Kb m Iu t iiM., ₍ Ii.. K (Mick IH'l'l M, - ti Ό - *. "*» -2- I) K 43 99 is doped with lithium oxide (Li ₇ O). 5. Functional element according to claim 1, characterized in that the device comprises comb-shaped electrodes, which generate elastic surface waves on the surface of the substrate for the acoustic-optical effect. 6. Functional element according to claim 1,:. thus identified-.Q indicates that the device comprises comb-shaped electrodes having a periodic refractive index distribution on the Generate substrate through the electro-optical effect. 7. Optical functional element with _{1 (} - a) a substrate the entire surface of which has been subjected to metal diffusion treatment; b) an optical waveguide, which by diffusion of protons on the surface of the substrate with the doped thereon Metal except for an area of the same. Is formed and c) a device for bringing about a modulation or deflection of propagating in the optical waveguide Light, the means having been provided at an area on the surface of the substrate where none Protons have been diffused in and which has the function of increasing the refractive index of the optical waveguide through external To change influences. 8. Functional element according to claim 7, characterized in that the substrate made of lithium niobate crystal or Lithium tantalate crystal is made. 30th 9. Functional element according to claim 8, characterized in that the metal is titanium. 10. Functional element according to claim 7, characterized indicates that the device comprises comb-shaped electrodes, -3- DE 4399 which generate elastic surface waves on the surface of the substrate for the acoustic-optical effect. 11. Functional element according to claim 7, characterized in that that the device comprises comb-shaped electrodes, which generate a periodic refractive index distribution on the substrate through the electro-optical effect. , Q 12. Method for producing an optical functional element according to one of the preceding claims, characterized in that one a) a mask on an area of the surface of the substrate forms that either from lithium niobate crystal - ₅ or lithium tantalate crystal is produced, b) an ion exchange process on the surface of the Performs substrate with the mask formed thereon to To inject protons into the substrate in an area where no mask has been formed and c) electrodes on the area formed with the Mask is covered. 13. The method according to claim 12, characterized in that that further a thermal diffusion treatment is applied to the entire surface of the substrate prior to the formation of the mask is subjected to a metal. 14. The method according to claim 13, characterized in that the substrate doped with protons further one thermal diffusion treatment is subjected. 15. The method according to claim 12, characterized in that the entire surface of the substrate is subjected to an external diffusion _{treatment with lithium oxide (Li 9} O) before the formation of the mask. -4- DK 4399 10. The method according to claim 12, characterized in that the ion exchange process is carried out by the substrate at a low temperature of a heat treatment g in a mixture of a carboxylic acid with a degree of dissociation in the range from 10 "to 10 and a lithium salt the carboxylic acid undergoes. 17. The method according to claim 16, characterized in that , Q that the lithium salt of the carboxylic acid in a molar ratio from 0.1 S to 3 I, based on the total amount of the mixture is added. 18. A method for producing an optical functional _{1 (} element according to one of the preceding claims, characterized in that one • a) Electrodes on an area of the surface of the substrate that forms either from lithium niobate or lithium tantalate is made and b) performing an ion exchange process on the surface of the substrate with the electrodes formed thereon, to inject protons into the substrate in an area not covered with the electrodes. _o _ 19. The method according to claim 18, characterized in that the entire surface of the substrate has been subjected to a thermal diffusion treatment with a metal prior to the formation of the electrodes. 20. The method according to claim 19, characterized in 30 that further the substrate doped with protons is subjected to a thermal diffusion treatment. 21. The method according to claim 18, characterized in that further the entire surface of the substrate before Formation of the electrodes of an external diffusion treatment -5- DE 4399 with lithium oxide (Li ₉ O) is subjected. 22. The method according to claim 18, characterized in that the ion exchange process is carried out by the substrate at a low temperature in a mi Schung a carboxylic acid with a degree of dissociation in the range from 10 ~ to 10 and a lit. acid is subjected to heat treatment. 23. The method according to claim 22, characterized in that that the lithium salt of the carboxylic acid is mixed in in a molar proportion of 0.1 to 3 %, based on the total amount of the mixture.